This application is a divisional application of U.S. application Ser. No. 09/435,718, filed Nov. 8, 1999 now U.S. Pat. No. 6,826,991.
The present invention relates to flexible sheet dispensers for sequentially dispensing a web of material from a plurality of rolls, and in particular to an automatic transfer mechanism for transferring the feed supply from a working roll to a reserve roll, upon exhaustion of the working roll.
Dispensers for toweling are primarily designed to dispense either a continuous length of web material, folded paper towels, or rolls of paper towels. Continuous towels are generally made of a reusable material and form a towel loop outside of the dispenser cabinet for the consumer to use. Folded towels are paper towels which are pre-cut and folded into various configurations to be individually dispensed for use. Roll towels are continuous rolls of paper toweling which are typically wound around a cardboard core and which are, upon dispensing, separated into and delivered as individual lengths of material.
Continuous web dispensers, such as those disclosed in U.S. Pat. No. 2,930,663 to Weiss and U.S. Pat. No. 3,858,951 to Rasmussen, require the user to pull on the loop of exposed toweling in order to cause a length of clean toweling to be dispensed and the exposed soiled toweling to be correspondingly taken up within the dispenser. Although economical, the continuous exposure of the soiled toweling is deemed unsightly, and therefore unacceptable to many consumers when compared to many available alternatives. Further, the exposure and possible reuse of soiled toweling may present additional health hazards and sanitation and hygiene concerns which should be avoided.
The use of either interfolded paper towels or C-fold paper towels eliminates some of the potential health risks associated with continuous web toweling. Dispensers for folded paper towels allow a user to pull the exposed end of a new individual towel in order to dispense the towel. These dispensers, such as the one disclosed in U.S. Pat. No. 3,269,592 to Slye et al., are also easy to refill with folded towels. That is, when the dispenser is partially empty, the cover can simply be removed and the remaining stack of towels can be replenished through the open top. Folded towels are, however, not usually the most economical alternative for institutional and other high-volume situations due to the uncontrolled dispensation of toweling.
Roll towels are cheaper to manufacture than folded towels and also eliminate the potential health and sanitation problems associated with continuous web toweling systems. Dispensers for roll towels usually include a lever, crank, or other user-activated mechanism for dispensing a length of towel. An effective and popular style roll towel dispenser is disclosed in commonly owned U.S. Pat. No. 4,712,461 to the present inventor. The '461 patent teaches the use of a blade that is cam actuated from within a feed roller to sever lengths of towel from the roll. In contrast to folded towel dispensers, it is not a straight forward matter to replenish a partially depleted supply of web material in a roll dispenser. If a new roll is substituted for a partially depleted or “stub” roll which is thrown away, substantial waste of material can result. If waste is avoided by letting the stub roll become completely depleted, then the dispenser may sit empty for some time before the roll is replaced, thereby causing inconvenience to users.
To overcome the problem of stub roll waste, roll dispensers have been designed to dispense two rolls of web material sequentially such that upon depletion of a primary roll, feeding from a reserve roll is commenced. Prior art systems have accomplished this transfer by either modifying the end of the web material or modifying the roll core upon which the web material is wound, such as in the system disclosed in U.S. Pat. No. 3,288,387 to Craven, Jr. Alternatively, the system of U.S. Pat. No. 3,628,743 to Bastian et al. senses the diameter of the primary roll in order to activate the transfer to the reserve roll, and the system of U.S. Pat. No. 3,917,191 to Graham, Jr. et al. senses the tension in the primary roll in order to detect when it is nearly exhausted. Unfortunately, tension responsive transfers are not particularly reliable since conditions other than reaching the end of the roll can trigger their operation, such as the slackening of the web or a break in the web material. Diameter responsive transfers also have a drawback in that the reserve web begins dispensing prior to the complete exhaustion of the primary roll. Thus, for at least a short time web material is dispensed simultaneously from both rolls, and again a waste of material results.
To overcome these disadvantages, the systems of U.S. Pat. No. 4,165,138 to Hedge et al. and U.S. Pat. No. 4,378,912 to Perrin et al. provide a transfer mechanism which senses the absence or presence of paper around a grooved feed roll by using a sensing finger which rides along the top surface of the web material and which then drops down into the groove in the feed roll when the trailing end of the primary web has passed thereover and thus uncovers the groove. Responsive to the movement of the sensing finger into the groove, the reserve web is introduced into the feed nip between the feed rolls and dispensing from the reserve roll begins. This type of transfer mechanism generally eliminates the false transfer associated with tension responsive systems, and reduces the amount of double sheet dispensing which occurs in other prior art diameter and end of roll responsive systems.
However, the use of sensing fingers riding on the web material can, depending on the design, produce extra friction which can inadvertently tear the web. Also, the introduction of additional components to sense the absence of the web and transfer the reserve web into the feed nip between the feed rollers creates additional opportunities for a transfer failure or interference with web feed to occur. In particular, in each of the designs of the Hedge et al. and Perrin et al. patents, a tucking device (blade or roll) is used. The device pivots into close proximity to the feed nip, and remains there through subsequent dispensing from the reserve roll. It is evident that interference with the web feed from the reserve roll could result if proper positioning of the transfer device, away from the nip, is not maintained.
A need has therefore existed for a flexible sheet dispenser having an automatic transfer mechanism which, in addition to eliminating or reducing simultaneous dispensing from two rolls, requires few additional parts within the dispenser and which is not prone to interference with the proper dispensing of web material. A transfer mechanism that, to a large extent, fulfills this need is described in commonly assigned U.S. Pat. No. 5,526,973 to Boone et al. Therein, movement and interengagement of one grooved feed roller relative to the other, upon depletion of a stub roll, actuates a transfer mechanism that introduces a reserve web into the feed nip. While generally quite effective, the movement and spring biasing of a relatively high mass feed roller can lead to difficulties. The feed roller spring bias force must be within a relatively narrow window. If the spring bias is set too high, the biasing force may inhibit smooth feeding of the web material through the rollers, and result in tearing of the web material. If it is set too low, the mechanism may not actuate effectively to cause a transfer of feed to the reserve roll immediately upon depletion of the stub roll. Over time, the spring bias provided to move one roll relative to the other is prone to eventually decrease, e.g., due to fatigue of the spring, such that ultimately the spring force may fall below the required relatively narrow range and thus be insufficient to properly actuate a web transfer.
Thus, there remained a need for an automatic web transfer mechanism that could provide increased reliability, robustness and cost effectiveness. A mechanism capable of delivering these characteristics is disclosed in commonly owned U.S. patent application Ser. No. 09/383,019 by Jespersen, filed Aug. 25, 1999, now U.S. Pat. No. 6,354,533. The sheet material dispenser disclosed in the Jespersen application uses a web transfer arm that remains positioned away from the feed path of the transferred web, to thus reduce the possibility of the transfer mechanism interfering with the web material as it is dispensed. The dispenser eliminates double sheet dispensing from the reserve and working rolls by sensing the presence or absence of the working web at the backside of the main feed roller.
Despite their benefits, the transfer mechanisms of the Boone et al. '973 patent and the Jespersen application are not well suited for providing a transfer of web feed in a dispenser with a feed mechanism incorporating an automatic cutting knife within the main feed roller. As mentioned above, commonly owned Rasmussen U.S. Pat. No. 4,712,461 teaches the use of a cam actuated cutting knife that progressively emerges from the feed roller as the roller rotates through a dispensing cycle. Use of a web sensor positioned against or near a feed roller having an integral web cutting knife, as taught in the '461 patent, would be problematic due to the emergence of the cutting knife as the feed roll rotates.
Dispensers embodying feed roller/cutter configurations in accordance with the Rasmussen '461 patent, such as the commercially available Georgia-Pacific P-12 dispenser, are popular, and large numbers are in use. To reduce material waste and associated costs, it would be highly desirable to provide a web transfer mechanism that may be manufactured as an adaption of, or retrofit to, these and like dispensers having a feed roller incorporated cutting knife, to thus provide a reliable and robust dispenser that combines effective web cutting and web feed transfer functionalities.